In motor vehicles, vibration dampers are mostly applied in the form of hydraulic-mechanical dampers and are provided particularly between a respective vehicle body and the axles of the respective motor vehicle. On the one hand, a vibration damper placed at this location prevents rocking and after-vibration of the vehicle body when excited by the roadway or over the course of certain driving states and, on the other hand, brings about a rapid attenuation of a vibration that is excited in a respective vehicle wheel by the roadway so that road grip of this vehicle wheel can always be guaranteed.
Vibration dampers are commonly constructed as telescoping shock absorbers in the form of mono-tube dampers or twin-tube dampers. A damping action is achieved through displacement of a damping medium, usually in the form of a hydraulic fluid, and the flow of the damping medium is influenced over the course of the displacement usually via a piston rod which is provided with a plurality of passages for this purpose. Damping characteristic curves of the vibration damper are then usually adjusted via hydraulic resistances which correspondingly influence the flow of the damping medium via the passages and which are often constructed as valve disks which are preloaded against a piston body of the piston valve. Spring elements are provided among others for preloading the valve disks and always guarantee a sufficient preloading of the valve disks. However, a reliable centering of the spring elements must be ensured because faulty assembly and, therefore, diverging valve characteristics can otherwise occur in batch fabrication.
DE 10 2007 004 149 A1 shows a piston valve for a vibration damper comprising a piston body with a plurality of passages extending axially through the piston body. A plurality of valve disks are preloaded against a respective valve seat at the piston body in the region of orifices of the passages, the preloading being brought about by an associated preloading device. This preloading device comprises a disk spring and a radially inner, annular centering disk which forms a centering device for the disk spring and ensures an inner centering of the disk spring on a piston rod neck on which the piston body is also guided. However, a spring is additionally provided because the disk spring can move axially relative to the centering disk in the course of assembling the piston valve, which can result in a faulty assembly of the piston valve during preloading of the piston valve via a fastening nut. This spring preloads the centering disk against a supporting disk of the piston valve and accordingly always holds the latter in a position in which the centering disk can realize its centering function.
Proceeding from the prior art described above, it is an object of the present invention to provide a preloading device for a piston valve by which a reliable inner centering of a spring element can be ensured over the course of assembling the piston valve, but which can be placed with low expenditure on assembly at the same time.
According to the invention, a preloading device comprises a spring element which is fitted by an inner diameter onto a radially inner centering device. The centering device serves for inner centering of the spring element in the installed state of the preloading device in a piston valve. According to the invention, a preloading device of this type is then preferably applied in a piston valve which comprises a piston body with at least one passage extending axially through the piston body. This at least one passage can be covered at the orifice thereof by at least one valve disk which is preloaded against the piston body by means of a preloading device according to the invention.
Within the meaning of the invention, an “inner centering” of the spring element of the preloading device means a guiding of the spring element at its inner diameter by means of the radially inner centering device in order to hold this spring element in the correct position during the assembly of the piston valve. In particular, the radially inner centering device centers the spring element during assembly of the piston valve indirectly on a piston rod neck of a piston rod of the vibration damper.
The invention includes the technical teaching that the spring element is axially fixed at the centering device via retaining means in that the retaining means at least partially enclose the spring element axially on both sides and are rigidly connected to the centering device in each instance. In other words, the spring element is held axially at the centering device by retaining means, for which purpose at least a portion of the spring element lies axially between the retaining means, and the retaining means are fixedly coupled to the centering device in each instance.
This type of configuration of a preloading device has the advantage that a pre-assemblable constructional unit is consequently furnished and is simply provided on the piston rod of the respective vibration damper in the course of assembling the piston valve, and a reliable inner centering of the spring element is always ensured as a result of the relative fixing of the spring element with respect to the radially inner centering device. With the aid of the retaining means, the spring element is fixed to the centering device in a positive engagement in axial direction due to the fact that it is at least partially axially enclosed and accordingly always remains with its inner diameter correctly positioned with respect to the centering device. This can prevent the spring element from creeping axially out of the centering device in an unwanted manner in the course of assembling the piston valve so as to rule out the risk of a faulty assembly of the spring element as a result of deficient inner centering. Further, owing to the arrangement of the preloading device as a pre-assemblable constructional unit, expenditure on assembly is reduced because it need merely be fitted on additionally as a unit, i.e., positioned on the piston rod neck.
In the case of DE 10 2007 004 149 A1, a reliable inner centering of the spring element is also ensured in that the centering disk defining the centering portion is preloaded against a supporting disk of the piston valve via a spring. However, assembly of this preloading device is more complicated because the individual parts must be placed successively during assembly and a preassembled unit is not formed. Further, faulty assembly cannot be entirely ruled out in spite of the preloading of the centering disk because relative movements between the centering disk and the spring element are possible in principle.
According to the invention, “radial” means an orientation along a radius of the spring element, while “axial” means an orientation in a tensioning direction of the spring element, which in the installed state of the preloading device corresponds to an orientation in direction of a longitudinal central axis of a piston rod of the vibration damper.
Further, the retaining means “at least partially” enclosing the spring element axially on both sides means that the retaining means radially overlap the spring element at least over a portion of the extension of the spring element and are provided in axial direction respectively on each side of the spring element. However, at least one of the retaining means can also completely overlap the axially adjacent spring element in radial direction.
Finally, the phrase “rigid connection” between the retaining means and the centering portion includes the meaning that the respective retaining means and the centering portion are fixedly coupled with one another at least in axial and radial direction. In a particularly preferred manner, however, the respective retaining means are immovable in their entirety with respect to the centering portion, which can be realized by a corresponding connection or also by means of an integral construction.
In accordance with an embodiment form of the invention, the centering device is formed by a centering disk which guides the spring element at an outer diameter. In this case, the inner centering of the spring element is realized via a corresponding disk which is provided radially inwardly of the spring element and to which the retaining means are connected. Consequently, a preloading device which is particularly compact axially can be implemented.
According to an alternative embodiment form of the invention, the centering device is formed by an outer diameter of an axially projecting flange portion of a supporting disk which is additionally defined by a radially extending shoulder portion of one of the retaining means. Accordingly, in this case the inner centering is realized via a correspondingly configured supporting disk which, together with a further supporting disk, serves inside a piston rod to intermediately receive the piston body, the spring elements and the valve disks. In this respect, the inner centering and the supporting function can be combined in one component part which, with the shoulder portion, forms an axial contact for the spring element.
In a further development of the above-mentioned embodiment form, the supporting disk is provided on an axial side remote of the flange portion with a hex exterior and is further outfitted with an internal thread at an inner diameter at least along a portion of its extension. In this way, the function of a fastening nut can be additionally integrated allowing a further reduction in the quantity of component parts, by which a further simplification of assembly can be realized.
According to a further embodiment form of the invention, at least one of the retaining means is formed in each instance by a retaining disk which is connected to the centering device. Consequently, particularly in case the centering device is formed by a centering disk, there are to be two retaining disks of this kind provided which are to be connected to the centering disk after the spring element and centering disk are positioned relative to one another in a corresponding manner. In case the centering device is formed via a supporting disk, however, only one retaining disk is to be provided.
In a further development of the invention, the spring element is enclosed axially between the retaining means only in the region of its inner diameter. Accordingly, the spring element can be inserted loosely between the retaining means so that the connection of the retaining means to the centering device is not loaded by a preloading force of the spring element. A preloading of the spring element is then first carried out during assembly of the piston valve and application of a clamping force via the respective fastening nut.
In accordance with an alternative embodiment of the invention, one of the retaining means is formed by a valve disk which is connected to the centering device and to which a preloading force is applied through the spring element. Accordingly, in this case one of the retaining means is formed directly by one of the valve disks to be preloaded allowing a further integration of functions. However, in this case a preloading of the spring element is carried out already during the formation of the preassembled constructional unit and consequently the connection of the valve disk to the centering device is also loaded by the preloading force of the spring element.
In a further development of the invention at least one of the retaining means is connected to the centering device by means of a joining process. This joining process is preferably a welding of the two components, for example, laser welding; however, another kind of welding method is also conceivable, as is soldering, gluing or an interference fit. Further, at least one of the retaining means can also be formed integral with the centering device.
In a further embodiment form of the invention, the spring element is a disk spring. A preloading of the at least one valve disk of the piston valve can be realized in an axially compact manner by means of a disk spring. Alternatively, however, the spring element can also be constructed in some other way, for example, as a corrugated spring or a helical spring, and in the latter case preferably has a conical cross section.
The invention is not limited to the combination of features specified in the main claim or the claims depending on the latter. Further, there are possibilities for combining individual features also insofar as they follow from the claims, the following description of preferred embodiment forms or directly from the drawings. Reference made to the drawings in the claims by the use of reference numerals is not intended to limit the scope of protection of the claims.